Effective armor technologies have been sought for many decades to protect humans, vehicles, and equipment against threats including projectiles, fragmentation, and blast damage.
Current body armor typically incorporates ceramic plates (Small Arms Protective Inserts/Enhanced Small Arms Protective Inserts, i.e., SAPI/ESAPI) backed by ultra-high-molecular-weight polyethylene (UHMWPE). These plates are effective against threats up to .30 caliber M2AP bullets. Currently, SAPI/ESAPI plates are considered to be one of the highest mass efficiency armor systems available through a synergistic interaction between the front ceramic plate and textile backing fabric.
Ceramics applied to armor designs perform well in defeating sharp, hardened ogives due to their high hardness and compressive strength. Limitations to ceramics include both lower tensile strength (i.e., on the order of 1/10 of their compression strength) and high shock velocities (i.e., greater than 15,000 fps). Typically, the compressive wave generated from a ballistic impact travels at a much faster velocity than the incident impact velocity. Due to the higher velocity, the compressive wave can reflect from the back surface of the ceramic forming a tensile wave. In addition to the back surface reflection, additional reflections occur within the formed impact crater. When two reflected rarefaction waves combine and exceed the tensile strength of the material, spall will occur. The spall will typically cause breakup of the ceramic well before the time it would take for the projectile to penetrate through the ceramic. Due to the short time duration required, only a fraction of the ceramic has been penetrated by the projectile by the time spall occurs. For this reason, ceramic armor typically is provided with a backing comprising an ultra-high-molecular-weight polyethylene (UHMWPE) material layer and/or is wrapped in a ballistic-rated body armor fabric. Such fabrics may include fibers comprising fiberglass, carbon fiber, aramid fiber, nylon, polyolefin, polyester, and UHMWPE. The backing material is able to arrest the incident projectile after penetrating the front ceramic plate. Typically, the longer than the ceramic can remain as a solid, the greater the performance of the ceramic to slow down or arrest the projectile. The increased performance of the ceramic reduces both the amount of backing material required and the blunt force trauma from a ballistic impact.
Excessive weight of armor used in personnel protective equipment is linked to fatigue and decreased mobility in personnel over the short term, and chronic injuries and degenerative conditions over the long term. These issues can also lead to lack of compliance with recommended armor use in personnel, increasing the risk of serious injury in the event of an impact. Excessive armor weight also results in premature failure of vehicles and equipment due to increased wear-and-tear.
In the search for a solution to these problems, and in particular the problem of excessive weight in armor used in personnel protective equipment, various approaches have been taken to improve existing armor.
U.S. Pat. No. 3,771,418 describes an anti-spall lightweight armor for military vehicles that includes a shock-absorbent layered combination of materials comprising an outer layer having a tensile strength of between 104 and 106 pounds per square inch, and an elastic modulus of between 105 and 108 pounds per square inch, and a deformable inner layer rigidly adhered to said outer layer, wherein the material constituting the outer layer possesses both a higher tensile strength and a higher elastic modulus than the material constituting the inner layer. The inner layer spreads a shock wave resulting from an impact over a spherical area that is at least 100 times greater in size than the spherical area that the outer layer presents to the wave front.
U.S. Pat. No. 7,540,228 describes an armor for protection against large caliber projectiles that has a ceramic layer with a confinement layer on a front thereof. The ceramic layer is backed by a first metallic layer and the first metallic layer in turn is backed by a composite layer. The composite layer is backed by a second metallic layer, which in turn is backed by an anti-trauma layer. The armor is used to protect personnel, but it can also be used to protect objectives such as vehicles.
U.S. Pat. No. 8,580,387 describes a composite armor including a ballistic armor layer and a directly attached polyurea layer. The polyurea layer is the cured reaction product of an isocyanate curing agent and a mixture of diamines. In a preferred embodiment, the polyurea layer is the strike face. The composite armor is useful for light armor applications in which weight is a factor, such as military vehicle armor and military boat armor.
U.S. Pat. Nos. 8,746,122 and 9,207,048 describe armor systems with a composite laminate having at least four alternating layers (two bi-layers) of a first material and a second material, the first material having a lower acoustic impedance than the second material. The first material is a viscoelastic polymer with a glass transition temperature less than the expected operational temperature range, and the second material can be a hard material such as steel, aluminum, or ceramic. The laminate can include many alternating layers of elastomer and hard material, and can be adhered or affixed to a thicker armor substrate. The second material layer can be a layer of hollow or solid spheres. Additional protective elements such as corrugated metal-ceramic panels and armored glass cylinders can be added to improve resistance to armor piercing rounds, explosively formed penetrators, or other threats.
U.S. Patent Appl. Publ. No. 2012/0312150 describes a body armor composite material provided to protect a wearer from small-arms projectiles. The material includes a flexible liner, a polymer binder disposed on the liner, and ceramic solids embedded in the binder. The flexible liner conforms to a portion of the wearer and elastically deforms in response to application of mechanical force. The binder can be a polyurea foam. The solids can be spheres arranged in a single-layer pattern substantially parallel to liner.
U.S. Patent Appl. Publ. No. 2015/0377592 describes a lightweight armor system providing blast protection and ballistic protection against small arms fire, suitable for use in helmets, personnel or vehicle protection, and other armor systems. A hard substrate is coated on the front surface with a thin elastomeric polymer layer, in which hollow ceramic or metal spheres are encapsulated. The coating layer having a thin elastomeric polymer layer with encapsulated metal or ceramic hollow spheres can be stand-alone blast protection, or can be added to an underlying structure. The glass transition temperature of the polymer is preferably between −50° C. and 0° C.
New materials have also been developed.
U.S. Pat. Nos. 8,815,408 and 9,314,996 describe composite materials comprising hollow metallic shells and a solid metal foam matrix. The metal foam composites show high strength, while maintaining a favorable strength to density ratio. The composite metal foams can be prepared by various techniques, such as powder metallurgy, and casting (including aspiration casting).
Deep Springs Technology describes applications for light-weight syntactic armor materials (LSAM) materials consisting of small, hollow silicon carbide shells encapsulated in a light-weight metal matrix on its company website. The website indicates that the composites may supplement existing armor systems and increase their effectiveness by reducing system weight while increasing blast mitigation properties. The Deep Springs Technology website states that it seeks to integrate LSAMs into military vehicles that are overburdened by current armor solutions.
In contrast to the armor materials and armor systems described in the prior art, the present invention beneficially provides composite armor and armor systems incorporating substrates that reduce and/or delay compressive waves associated with ballistic impacts from reflecting off of the back surface of the armor material as tensile waves, which may damage or destroy the front face material. The armor materials, systems, and methods of the invention beneficially exhibit increased mass efficiency and reduce blunt force trauma resulting from ballistic impacts.